under consideration (for more, see consideration): Consideration is when the person receiving/having power is still considering or deciding whether to accept the lesser-power partner to a closer, more important, or more responsible (etc.) position or relationship: slave, 24/7 or collaring are common.
unicorn: “The elusive, mythical creature that is a bi-female willing to join a couple for the perfect MFF (male/female/female) threesome.” also someone whom you have fantasized having such perfect exquisite sex with SO much that the reality will never live up to your expectations.
uniform play: Role play in which the wearing of uniforms, such as military or medical uniforms, is a significant part of the role play.
urethral play: Play involving the urinary passage. Commonly uses sounds orcatheters. Caution: the urethra and bladder are extremely prone to damage and infection. Women are especially prone to infection, as the urethra is only a few inches long, and contamination can more easily enter the bladder. A person should void their bladder as forcefully as possible immediately after urethral play, as urine will help to flush out contaminants.
urethral sound A smooth rod, usually metal, for insertion in the urinary passage; comes in a set of graduated sizes. Medically used for expanding the urethra in cases of genital defect, or damage resulting from illness or injury. In BDSM, used for urethral play.